1. Field of the Invention
The present invention relates to a bipolar-CMOS (CMOS: Complementary Metal-Oxide-Semiconductor) semiconductor device wherein bipolar transistors and P- and N-channel type MOS field effect transistors are formed on a single semiconductor chip, and more particularly to an improvement of a bipolar-CMOS semiconductor device for enhancing its integration level.
2. Description of the Related Art
Heretofore, in a bipolar-CMOS semiconductor device, it was necessary to adopt a structure isolating the bipolar transistor from the substrate in order to take out a collector potential of an NPN bipolar transistor. For this reason, it was necessary to electrically isolate the collector of the bipolar transistor with a selectively oxidized layer or a P type semiconductor region, which led to a drawback in that the level of integration density is lowered considerably as compared to that of a genuine CMOS IC.